lib/vsprintf: add %*pE[achnops] format specifier

lib/vsprintf: add %*pE[achnops] format specifier

This allows user to print a given buffer as an escaped string.  The
rules are applied according to an optional mix of flags provided by
additional format letters.

For example, if the given buffer is:

    1b 62 20 5c 43 07 22 90 0d 5d

The result strings would be:
    %*pE            "\eb \C\a"\220\r]"
    %*pEhp          "\x1bb \C\x07"\x90\x0d]"
    %*pEa           "\e\142\040\\\103\a\042\220\r\135"

Please, read Documentation/printk-formats.txt and lib/string_helpers.c
kernel documentation to get further information.

[[email protected]: tidy up comment layout, per Joe]
Signed-off-by: Andy Shevchenko <[email protected]>
Suggested-by: Joe Perches <[email protected]>
Cc: "John W . Linville" <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>